1. Field of the Invention
The present invention relates to a system for draining fluids from the body cavity of a patient, and more specifically to an apparatus for automatically regulating negative pressure in the collection chamber of the system during operation to prevent exposing the patient to dangerously high negative pressure levels. More particularly, this invention relates to an air flow sensitive, buoyant valve that closes when a patient generates the required high air flow rate in the system because of a patient's inspiration, or it shuttles between open and closed positions when a low air flow rate generates excess negative pressure inside the collection chamber.
2. Prior Art
A chest drainage unit is an apparatus for suctioning gases and liquids from the pleural cavity of patients. The pleural cavity lies within the rib cage above the diaphragm and is surrounded by the pleural membrane. The pleural cavity contains both lungs, which in their normal expanded state fill the pleural cavity. Several conditions and diseases such as interventional surgery, trauma, emphysema and various infections can cause a build up of liquid and gases around the lungs in the intrapleural space. When this happens, it causes the lungs to collapse to a volume much less than that of the pleural cavity, thereby severely impairing breathing functions of the patient. The lungs can be re-expanded to their normal state to fill the pleural cavity by draining the liquid and gases from the intrapleural space using a chest drainage unit.
Chest drainage units are also used during autotransfusion for recovering autologous blood from the patient's pleural and mediastinal cavities and transfusing that blood back into the patient. Autotransfusion offers significant advantages over normal transfusion procedures which use homologous blood from other humans. Autologous blood reduces the risk of adverse reactions and transmission of infectious disease while supplying a readily available and safe source of compatible blood to the patient. For these reasons, chest drainage units are being designed to both evacuate fluids from the intrapleural space and autotransfuse shed autologous blood back into the patient.
Various devices have been developed to drain and collect fluids such as blood from the intrapleural space for subsequent autotransfusion. U.S. Pat. No. 4,857,042 to Schneider illustrates the prior art development of autotransfusion chest drainage units. The device includes a collection chamber for the collection of fluid from the pleural cavity, a water seal chamber for preventing passage of gas from the atmosphere into the patient's pleural and mediastinal cavities, and a manometer chamber for regulating the degree of vacuum in the system. An inlet port of the collection chamber is connected to the patient's pleural cavity via a thoracotomy tube that deposits shed blood and gases into the collection chamber. The device is also connected to a blood compatible pump at an outlet port of the collection chamber for pumping autologous blood back into the patient. The Schneider device is also provided with a valve mechanism above the water seal chamber to permit the passage of fluids from the water seal chamber in the event of a sudden increase in negative pressure inside the collection chamber, such as when the patient inhales, or blood is withdrawn from the collection chamber with a blood pump or other similar device.
One drawback with the Schneider device is that no provision is made for autotransfusing simultaneously with draining the pleural cavity. Prior art drainage devices generally could not be used to simultaneously collect blood from the pleural and mediastinal cavities and autotransfuse, because there was no provision for automatic regulation of negative pressure during autotransfusion. During continuous autotransfusion, as fluid exits the collection chamber, the remaining fluid volume falls and pressure level concurrently drops within the collection chamber and pleural cavity. It is therefore vital that negative pressure within the collection chamber be maintained within a relatively narrow range to keep bleeding to a minimum and prevent any damage to the intrathoracic tissue which might occur. It is also important to maintain negative pressure within a relatively narrow range in order to prevent water from being transferred out of the water seal chamber and into the collection chamber due to loss of vacuum therein. Permanent loss of water in this manner would render the water seal useless as a one way valve for gases passing out of the collection chamber.
One approach in solving this problem is to provide a collapsible bag whose volume can change as required. U.S. Pat. No. 4,443,220 to Hauer et al. discloses such a bag which may be removed from the drainage device when full and placed on a stand to effect reinfusion, however this type of device is incapable of simultaneous drainage and reinfusion. Another method is illustrated by U.S. Pat. No. 4,548,413 to Russo wherein a mechanical pressure regulating mechanism in communication with the collection chamber is provided which regulates the sub-atmospheric pressure in the collection chamber independent of the chamber's effective volume. Unfortunately, such regulating mechanisms are costly and often unreliable.
A further problem also arises with the drainage tube which connects the patient to the drainage device. The drainage tube from a patient may itself cause a significant increase in negative pressure in the collection chamber when a nurse attempts to clear or "strip" away any occlusions blocking the tube. "Stripping" is where a nurse or practitioner clears the tube's passageway of blockages that occlude the tube by pinching off a portion of the tube nearest the patient, moving the pinch along the tubing towards the inlet port of the CDU, and then releasing the pinch. This "stripping" action forces any blockages along the tube, but also introduces substantial fluctuations in pressure inside the drainage device due to the sudden release of low pressure in the tube after the pinch is released.
Prior art drainage devices are also designed to permit a patient to draw as much vacuum pressure as is required for both normal and deep inspiration without transferring water from the water seal chamber into the collection chamber. Prior art devices have included push button type valves in communication with the collection chamber for manually venting excess negative pressure inside the drainage device. However, problems exist with manual venting.
One problem associated with manual venting of excess negative pressure is that known venting systems do not give an inherent indication that a high vacuum is present in the collection chamber. Another problem associated with manual venting of excess vacuum is that the nurse must manually push down on the push button valve in order to allow atmospheric air to vent inside the collection chamber. Such a procedure can take upwards of a full minute and requires the nurse to apply constant pressure on the push button valve during release. Further, the nurse must carefully observe and coordinate the level of the water seal with the release of vacuum on the push button valve. Without careful observation and coordination of the manual pressure release during gravity drainage of the collection chamber, the patient's intrathoracic vacuum could be lowered to dangerously low level, such as atmospheric pressure, and cause a serious clinical event to the patient known as a pneumothorax.
One approach to the solution of venting excess negative pressure from the drainage device is illustrated in U.S. Pat. No. 5,114,416 to Karwoski et al. The Karwoski et al. device discloses a float valve mechanism interposed between the water seal chamber and the collection chamber that provides for automatic controlled release of excess vacuum beyond that required for patient inspiration. The Karwoski et al float valve allows the patient to draw high vacuum in the collection chamber for breathing while automatically releasing negative pressure when excessive vacuum is maintained for an extended period of time therein. The float valve includes a valve seat forming an aperture and buoyant ball that is adapted to seal against the aperture of the valve seat. During periods when high vacuum exists in the collection chamber due to patient inspiration or deep gasp exercises, water from the water seal chamber rises until it lifts and seats the ball against the valve seat. Once the ball is engaged, the aperture is shaped to permit the water to still pass therethrough but at a substantially reduced rate.
During periods of extended high, excessive vacuum in the collection chamber the water column becomes depleted as enough water is forced up one arm of the water seal chamber and passes through the aperture. Once through the aperture, the water flows into an overflow chamber and the height of the water column below becomes insufficient to maintain the ball valve in the seated position due to leakage of ambient air into the collection chamber following the final influx of water therethrough, thereby effecting automatic release of the valve. However, the Karwoski et al. device suffers from several drawbacks.
The Karwoski et al. floating valve is activated by hydraulic pressure of the water column from the water seal lifting and engaging the valve ball into the sealed position. Unfortunately, the design of the Karwoski et al. valve permits leakage of fluid when engaged in the sealed position. This leakage eventually allows air to flow into the collection chamber during extended deep gasp exercises and effectively lowers the negative pressure therein over time, thus making it difficult for the patient to maintain a constant negative pressure inside the collection chamber during the deep gasp exercise. During convalescence, it is preferable to maintain a constant negative pressure inside the pleural cavity in order to allow the patient to effectively exercise the diaphragm muscles under the cavity. Without a sufficient negative pressure, the diaphragm muscles are unable to exert enough muscular action against the pleural cavity due to the underinflated condition of the lungs.
The Karwoski et al. device also suffers from other drawbacks. Although this device provides automatic negative pressure relief during low flow situations like continuous autotransfusion, the valve is not designed to be air-flow sensitive and is incapable of maintaining excessive vacuum when the patient is performing extended deep gasp exercises. Often during convalescence of the pleural cavity, patients are required to perform deep gasp exercises in order to strengthen the diaphragm muscles beneath the lungs. In performing these exercises a sudden and high excessive vacuum is generated in the collection chamber when the patient takes a sudden and deep inspiration. When using the Karwoski et al. device, the patient is incapable of maintaining the required high vacuum inside the pleural cavity during an extended deep gasp exercise because the float valve does not remain closed. Instead, the valve leaks water after the water column from the water seal chamber engages and seals the float valve, and air continues to leak past the valve after the water is depleted. Thus, the Karwoski's float valve operates only when the water column is drawn upward and engages the valve into its sealed position, and the valve will always leak air even after the water column under it is depleted.
Accordingly, it is the principal object of the present invention to provide a fluid recovery system having an improved flow-sensitive, buoyant valve that provides for automatic and/or complete closure when a minimum amount of air flow is applied thereto.
Another important object of the present invention is to provide an air-flow sensitive valve that maintains substantially the same negative pressure inside the collection chamber of the apparatus as is being maintained in the patient's pleural cavity while the patient is performing deep gasp exercises.
It is also an object of the present invention is to provide an improved float valve that does not leak during operation.
Another further object of the present invention is to provide a buoyant valve that can operate to relieve excess negative pressure when there is a slow rate of increase in negative pressure within the apparatus.
It is a further object of the present invention to provide a buoyant valve that will shuttle between open and closed positions in such a manner that excess negative pressure is automatically relieved when there is a slow rate of increase in negative pressure.
Another object of the present invention is to provide a valve that combines the dual functions of relieving excess negative pressure during low flow rate conditions while maintaining equilibration of the collection chamber and pleural cavity pressures during high air flow rate conditions.